The present invention relates to a method for manufacturing a glass substrate of an information recording medium, such as a magnetic disk, a magneto-optic disc, or an optical disc. More specifically, the present invention relates to a method for manufacturing a glass substrate of an information recording medium that enables sufficient removal of abrasion material and glass chips without deforming the texture of the glass substrate surface and enables stable operation of a reading device.
In the prior art, a glass substrate of an information recording medium is immersed in a chemical reinforcement liquid, which is contained in a tank, to chemically reinforce the surface of the glass substrate. Thermally molten potassium nitrate (KNO3) is used as the chemical reinforcement liquid. Lithium ions (Li+) or sodium ions (Na+), which exist near the surface of the glass substrate, are exchanged with potassium ions (K+), the ion radius of which is greater than that of the lithium ions and the sodium ions. This forms a compression stress layer on the surface of the glass substrate and reinforces the glass substrate.
Subsequently, an abrasion tape is pressed against the surface of the glass substrate in the circumferential direction while feeding abrasion slurry, which includes diamonds, to the surface. This forms a linear texture that extends in the circumferential direction of the glass substrate.
After forming the texture, the glass substrate is washed by immersing the substrate in water or an alkali solution or by scrubbing the substrate as water or an alkali solution runs along the substrate.
Subsequent to the texture formation, glass chips and the abrasion material of the abrasion slurry remain on the surface of the glass substrate. Thus, the glass chips and abrasion material must be washed away and removed.
The linear texture, which extends in the circumferential direction of the glass substrate, is formed from fine embossments. Thus, the shape of the embossments may change when performing a physical or chemical process. The texture is not uniform. Thus, the texture may deform especially at portions that are narrow during the washing process. This would hinder the removal of abrasion material and glass chips subsequent to the texture formation. When using the glass substrate for a magnetic recording medium or the like, this may decrease the stability of a magnetic head, which reads magnetic data from the surface of the glass substrate. Further, the magnetic head may be lifted above the proper position. This may decrease the reading accuracy and damage the magnetic head.
Accordingly, it is an object of the present invention to provide a method for manufacturing a glass substrate of an information recording medium that enables stable operation of a reading device and sufficient removal of abrasion material and glass chips without deforming the texture of the glass substrate surface.
To achieve the above object, the present invention provides a method for manufacturing a glass substrate that is used as an information recording medium. The method includes preparing a disk-like glass substrate. The glass substrate is acid resistant. When an index of acid resistance is the maximum depth at which components other than silica dissolve from the glass substrate during immersion of the glass substrate in 1 percentage of weight of sulfuric acid, the acid resistance of the glass substrate is represented by the maximum depth of 0.5 nm to 10 nm. The method further includes forming a linear texture by pressing a tape against the glass substrate in a circumferential direction of the glass substrate while feeding abrasion slurry to the surface of the glass substrate, and performing acid treatment on the glass substrate on which the texture is formed.
A further aspect of the present invention is a disk-like glass substrate that is used as an information recording medium. The glass substrate includes a linear texture formed on a surface of the glass substrate. The glass substrate is acid resistant. When an index of acid resistance is the maximum depth at which components other than silica dissolve from the glass substrate during immersion of the glass substrate in 1 percentage of weight of sulfuric acid, the acid resistance of the glass substrate is represented by the maximum depth of 0.5 nm to 10 nm.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.